1. Field of the Invention
The invention generally relates to surge protection of coaxial cables and transmission lines. More particularly, the invention relates to a surge arrestor tunable for operation in a range of different frequency bands.
2. Description of Related Art
Electrical cables, for example coaxial transmission lines of antenna towers, are equipped with surge suppression equipment to provide an electrical path to ground for diversion of electrical current surges resulting from, for example, static discharge and/or lightning strikes.
Prior coaxial suppression equipment typically incorporated a frequency selective inductor shorting element between the inner and outer conductors dimensioned to be approximately one quarter of the frequency band center frequency in length, also known as a quarter wavelength stub. Therefore, frequencies within the operating band pass along the inner conductor, reflecting in phase from the quarter wavelength stub back to the inner conductor rather than being diverted to the outer conductor and/or a grounding connection. Frequencies outside of the operating band, such as low frequency surges from lightning strikes, do not reflect and are coupled to ground, preventing electrical damage to downstream components and/or equipment.
U.S. Pat. No. 5,982,602 “Surge Protector Connector” by Tellas et al, issued Nov. 9, 1999 commonly owned with the present application and hereby incorporated by reference in the entirety, is exemplary of prior frequency band specific surge arrestors. Separate design and manufacture is necessary to produce surge arrestors capable of operating at the various typical frequency bands of operation. Each surge arrestor, designed for a particular frequency band, has a specifically dimensioned spiral inductor stub, requiring the separate design and manufacture of multiple coaxial surge arrestor configurations for each of the various frequency bands.
Competition within the electrical cable, connector and associated accessory industries has focused attention on cost reductions resulting from increased manufacturing efficiencies, reduced installation requirements and simplification/overall number of discrete parts reduction.
Therefore, it is an object of the invention to provide an apparatus that overcomes deficiencies in the prior art.